The invention related to a method of operating a gas turbine having a combustion chamber, a turbine including at least two rows of blades, and an air compressor. Compressed air and fuel are fed to the combustion chamber and cooling air is fed to the turbine. The invention also relates to a gas turbine working, in particular, according to the method.
The invention relates, in particular, to a gas turbine that works in combination with a steam turbine such that exhaust gas flowing out of the gas turbine is utilized for providing high-pressure steam expanded in the steam turbine while performing mechanical work. Such combinations of gas turbines and steam turbines are realized, for example, in combined-cycle power plants; they permit the generation of electrical power with efficiencies of 50% and more.
A gas turbine is generally a combination of a compressor for air, at least one combustion chamber for burning a fuel with the air compressed by the compressor, and a turbine in the actual sense, in which the hot flue gas produced in the combustion chamber is expanded to perform work. As a rule, the compressor and the turbine are mechanically coupled to one another. The air compressor is frequently a turbocompressor.
During operation of a gas turbine, the blades of the turbine are normally cooled. Thus, a large number of documents disclose providing an open cooling system for forming film cooling with cooling air, the open cooling system directing the cooling air used for the cooling through the blades of the turbine. A portion of the compressed air is used as cooling air, which then discharges in the turbine from open blades and is admixed with the flue-gas flow. As a result of the outflow of the cooling air from guide and/or moving blades, the open air cooling of the blades leads to a reduction in the temperature of the flue gases inside the turbine and downstream of the turbine on the outflow side. Such a reduction in temperature reduces the efficiency of the gas turbine.
In addition, the thermodynamic efficiency of a combination of a gas turbine and a steam turbine is not only determined by the efficiency of the gas or steam turbine, but, to a great extent, is also dependent on the thermodynamic coupling of the two machines. An essential determining factor is the temperature of the exhaust gas flowing out of the gas turbine.
To achieve a high efficiency, the prior art includes heating the compressed air by indirect heat exchange with the exhaust gas from the turbine.
To increase the exhaust-gas temperature, a concept for a guide blade of a gas turbine is described in German Published, Non-Prosecuted Patent Application DE 43 30 613 A1. The concept disclosed therein directs a small fraction of fuel directly to the turbine in an open cooling system with the cooling air. As a result, interheating of the exhaust gas is achieved without expensive measures in terms of equipment, which leads to an increase in the efficiency.
Cooling concepts that direct cooling fluid in a closed system instead of in an open system likewise increase the efficiency.
For example, German Published, Non-Prosecuted Patent Application DE 196 21 385 A1 discloses directing a first substance for cooling the guide blades in a closed cooling system in a guide blade and a moving blade. The first substance endothermically reacts with a second substance. The energy required for an endothermic reaction can preferably be effected by the absorption of heat from the hot flue-gas flow. The reaction product is then fed to the combustion chamber. The chemically bonded reaction energy and the heat absorbed by the substances are released in the combustion process. The release reduces the fuel consumption and, consequently, increases the efficiency of the gas turbine.
It is accordingly an object of the invention to provide a fuel preheating in a gas turbine that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that provides a fuel preheating method that achieves a good cooling of the turbine blades and an increased efficiency, and a gas turbine suitable, in particular, for carrying out the method, the turbine having a high efficiency.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of operating a gas turbine, including the steps of providing a gas turbine having a combustion chamber, a turbine having at least two rows of blades, at least some of the blades having an interior defining first cavities and second cavities, and an air compressor, feeding compressed air and fuel to the combustion chamber, feeding cooling air to the turbine, directing at least a portion of fuel at least in a section of the blades through the first cavities and simultaneously preheating the portion of fuel before the portion of fuel is introduced into the combustion chamber, and directing cooling air fed to the turbine in a further section of the blades through the second cavities and discharging the cooling air at least partly at the blades.
The objectives of the invention are achieved with the method according to the invention by virtue of the fact that at least one portion of the fuel, before it is introduced into the combustion chamber, flows in a section of the blades through cavities formed in the interior space of the blades and in the process is preheated simultaneously. The thermal energy that is, thus, absorbed by the fuel advantageously no longer needs to be dissipated through a cooling fluid, for example, cooling air. The cooling air that is, thus, saved reduces the work of the air compressor, which otherwise would have to be performed by the turbine. In addition, preheated fuel passes into the combustion chamber. Consequently, the efficiency of the gas turbine is increased.
In accordance with another mode of the invention, the cavities formed in the blades and in which the fuel flows form a closed system relative to the interior of the gas turbine. The system ensures that the fuel no longer comes into contact with other flow media, such as, for example, a cooling fluid or the flue gas (action fluid). In particular, due to the closed system, uncontrolled combustion outside the combustion chamber is ruled out.
In accordance with a further mode of the invention, a very simple embodiment is characterized by the fact that the fuel successively flows through a plurality of rows, in particular, through all the rows, of blades and is then fed to the combustion chamber.
In accordance with an added mode of the invention, the fuel is fed separately, i.e., in separate flows, through a plurality of rows of blades and is then respectively fed separately or as a uniform flow to the combustion chamber. Such a fuel feed advantageously permits load-dependent control of the gas turbine.
In accordance with an additional mode of the invention, the cooling air fed to the turbine advantageously flows in a further section of the blades through other cavities formed in the interior space of the blades. The cooling air discharges at least partly at the blades in a preferred manner such that an air film forms on the outer surface of the blades.
In accordance with yet another mode of the invention, small fractions of fuel, which burn in the turbine, are preferably admixed with the cooling air to increase the temperature of the exhaust gas flowing out of the turbine.
With the objects of the invention in view, there is also provided gas turbine, including a combustion chamber, a turbine having at least two rows of blades, at least some of the blades having an interior defining first cavities and second cavities, an air compressor, a combustion-air line for feeding compressed air into the combustion chamber, the combustion-air line fluidically connected to the air compressor and the combustion chamber, a supply unit for supplying fuel, at least one fuel line for feeding fuel into the combustion chamber, the at least one fuel line fluidically connected to the combustion chamber and to the supply unit, at least one cooling-air line for feeding cooling air into the turbine, the at least one cooling-air line fluidically connected to the turbine and to the air compressor, the first cavities fluidically connected to the combustion chamber and to the supply unit for directing at least a portion of fuel to the combustion chamber from the supply unit through the first cavities at least in a section of the blades and, thereby, preheating the portion of fuel before being introduced into the combustion chamber, a system defined by the first cavities and the section of the blades being closed relative to an interior of the gas turbine, and the second cavities fluidically connected to the air compressor and receiving at least a portion of the cooling air through the second cavities for cooling the blades.
The gas turbine includes a combustion chamber, a turbine having at least two rows of blades, an air compressor, a combustion-air line for feeding compressed air, at least one fuel line for feeding fuel into the combustion chamber, and at least one cooling-air line for feeding cooling air into the turbine. The objectives of the invention are achieved in the gas turbine of the invention where at least a portion of the fuel is directed to the combustion chamber from a supply unit through cavities formed in the interior space of the blades and which, at least in a section of the blades, form a closed system relative to the interior of the gas turbine.
In accordance with yet a further feature of the invention, the fuel is preferably fed successively through a plurality of rows, in particular, through all the rows, of blades to the combustion chamber.
In accordance with a concomitant feature of the invention, alternatively, the fuel is preferably fed separately through a plurality of rows of blades and then respectively separately or as a uniform flow to the combustion chamber, a factor which, in particular, has an advantageous effect on the controllability of the gas turbine.
The advantages achieved with the invention include, in particular, the fact that, by feeding fuel through cavities that are formed in the interior space of the blades and that form a closed system relative to the interior of the gas turbine, the fuel absorbs thermal energy which otherwise would have to be dissipated by a cooling fluid. Where the fuel consumption is reduced by heating the fuel on one hand, cooling air for the turbine is saved on the other hand. And, the work of the air compressor that otherwise would have to be performed by the turbine is reduced. Consequently, the efficiency of the gas turbine is increased. In addition, efficiency losses in the turbine due to mixing of hot action fluid with cooling air are reduced due to the fact that cooling air discharges at the blades only to a reduced extent.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a fuel preheating in a gas turbine, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.